TITLE: Study of the microbial population associated to the fermentation process of arbequina cultivar table olives.

DIRECTORS: Cristina Reguant y Nicolas Rozès

In this thesis the ecology of the industrial fermentation process of arbequina table olives has been characterized at species level. The results show that it is established a dynamic equilibrium between lactic acid bacteria and yeasts. Initially there is also a significant number of Enterobacteriaceae that disappear as medium pH falls. Lactobacillus pentosus, Candida diddensiae and Candida boidinii were the main species identified. It has also been studied a spontaneous fermentation at pilot-scale observing the development of wild microorganisms of the olive fruit during the fermentation. In the laboratory fermentation salt and olive maturity effect were studied, noting that a higher salt concentration favored the disappearance of Enterobacteriaceae without affecting lactic acid bacteria development and a greater maturity favored lactic acid bacteria growing. Different starter cultures were followed by means of GTG5 PCR during controlled fermentations. Results showed L. pentosus as the most suitable species to be used as inoculum in the case of arbequina olives. It was observed too the benefits of using a yeast as co-inoculum to favor the imposition of the lactic bacteria and to provide microbial stability. It was studied the presence of plantaricin genes in a collection of isolates of L. paraplantarum, L. pentosus and L. plantarum. The three species have the same plantaricin genes and it was observed a relationship between the genes a strain posses and its isolation source. Transcriptional studies confirmed the importance of plantaricin S in L. pentosus B96 and the contribution of other bacteriocin genes to the total bioactivity of the strain.